Wide-node drive system

ABSTRACT

An electro-mechanical drive unit connectable with multiple power sources for launching and propelling a vehicle includes an output member, a stationary member, a gear-train, and a torque-transmitting device. The drive unit also includes a compound planetary gear arrangement having a first, second, third, and fourth junction points. The power sources include a first motor/generator and a second motor/generator. The second motor/generator is operatively connected to the compound planetary gear arrangement at the first junction point via the gear-train and the output member is operatively connected to the compound planetary gear arrangement at the second junction point. Additionally, the first motor/generator is operatively connected to the compound planetary gear arrangement at the fourth junction point. Furthermore, the torque-transmitting device is engageable to ground the third junction point to the stationary member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/555,784 filed on Nov. 4, 2011, which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

The disclosure relates to a wide-node drive unit for a vehicle.

BACKGROUND

To produce a more efficient vehicle, hybrid vehicle powertrains combinean electric motor and a conventional internal combustion engine. Torquefrom the engine and the electric motor is typically channeled to thevehicle's driven wheels via a transmission. Efficiency of a hybridvehicle powertrain is generally related to the percentage of time thatthe engine must be run in addition to or in place of the electric motorfor powering the vehicle.

Some hybrid powertrains employ a single electric motor in combinationwith the engine. In such powertrains, transmission output, as well asvehicle speed, is directly related to the speeds and torques of theengine and the electric motor. Other hybrid powertrains employ twoelectric motors in combination with the engine to power the vehicle.Additionally, a vehicle may employ purely electric propulsion. In such acase, the vehicle's powertrain will have one or more motor-generatorsand no internal combustion engine.

In either a hybrid or purely electric powertrain, the electric motorsare operatively connected to a transmission which includes planetarygearing such that torque and speed of the electric motors may beselected independently of vehicle speed and desired acceleration. In ahybrid powertrain, control of the engine is typically achieved byvarying individual torque contribution from the electric motor(s). Thus,such hybrid and purely electric powertrains may each provide selectabletorque contribution from their electric motors, and, in the case of thehybrid powertrain, may similarly provide a selectable torquecontribution from the engine to drive the subject vehicle.

SUMMARY

An electro-mechanical drive unit connectable with multiple power sourcesfor launching and propelling a vehicle includes an output member, astationary member, a gear-train, and a torque-transmitting device. Thedrive unit also includes a compound planetary gear arrangement havingfirst, second, third, and fourth junction points. The power sourcesinclude a first motor/generator and a second motor/generator. The secondmotor/generator is operatively connected to the compound planetary geararrangement at the first junction point via the gear-train, while theoutput member is operatively connected to the compound planetary geararrangement at the second junction point. Additionally, the firstmotor/generator is operatively connected to the compound planetary geararrangement at the fourth junction point. Furthermore, thetorque-transmitting device is engageable to ground the third junctionpoint to the stationary member.

The compound planetary gear arrangement may include a first planetarygear set interconnected with a second planetary gear set. In such acase, each respective first and second planetary gear set may include afirst, a second, and a third member, and wherein two members of thefirst planetary gear set may be operatively connected to two members ofthe second planetary gear set.

The first junction point may be defined by the first member of the firstplanetary gear set. The second junction point may be defined by thesecond member of the first planetary gear set interconnected with thefirst member of the second planetary gear set. The third junction pointmay be defined by the third member of the first planetary gear setinterconnected with the second member of the second planetary gear set.Furthermore, the fourth junction point may be defined by the thirdmember of the second planetary gear set.

In an alternative embodiment, the first junction point may be defined bythe first member of the first planetary gear set interconnected with thefirst member of the second planetary gear set. The second junction pointmay be defined by the second member of the first planetary gear set. Thethird junction point may be defined by the third member of the firstplanetary gear set interconnected with the second member of the secondplanetary gear set. Finally, the fourth junction point may be defined bythe third member of the second planetary gear set.

The first, second, third, and fourth junction points may provide atleast a 3 to 1 gear ratio spread between the torque-transmitting deviceand the output member. The highest numerical gear ratio in the driveunit may be approximately 4 to 1 and the lowest numerical gear ratio maybe approximately 0.7 to 1.

The first motor/generator may be disposed on a first rotating axis andthe second motor/generator may be disposed on a second rotating axis,wherein the first axis may be substantially parallel to the second axis.

The power sources may additionally include an internal combustionengine. In such a case, the engine may be disposed on the first rotatingaxis and be operatively connected to the compound planetary geararrangement at the third junction point.

The torque-transmitting device may be selectively engaged and disengagedvia an electrically actuated device. Additionally, thetorque-transmitting device may be one of a band, a roller-ramp, a dogclutch, and a sprag type of a brake. Accordingly, if the stationarymember is a housing of the electro-mechanical drive unit, thetorque-transmitting device may be used to brake the third junction pointrelative to the housing.

The second motor/generator may be configured to generate greater torqueand be physically larger than the first motor/generator. Additionally,the first motor/generator and the second motor/generator may employnon-rare earth magnets.

The drive unit may additionally include a first hydraulic pump and asecond hydraulic pump. In such a case, the first pump may be operativelyconnected to the third junction point and the second pump may beoperatively connected to the output member.

Such a drive unit in conjunction with the engine, the firstmotor/generator, and the second motor/generator may be part of a hybridpowertrain having the EVT that is configured to provide a single-modewide-node gear ratio spread configuration to launch and propel thevehicle.

The above features and advantages, and other features and advantages ofthe present disclosure, will be readily apparent from the followingdetailed description of the embodiment(s) and best mode(s) for carryingout the described invention when taken in connection with theaccompanying drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic stick diagram illustration of a wide-nodecompound-split electrically variable transmission (EVT) employed as partof a hybrid powertrain for a vehicle.

FIG. 2 is a schematic lever diagram illustration of the wide-node EVTpresented in stick diagram form in FIG. 1.

FIG. 3 is another embodiment of the schematic lever diagram illustrationof the wide-node EVT presented in stick diagram form in FIG. 1.

FIG. 4 is a schematic stick diagram illustration of another embodimentof a wide-node EVT employed as part of a hybrid powertrain for avehicle.

FIG. 5 is a schematic lever diagram illustration of the wide-node EVTpresented in stick diagram form in FIG. 4.

FIG. 6 is a graph illustrating a comparison of vehicle distance traveledper engine revolution for the wide-node EVTs shown in FIGS. 1-5.

DETAILED DESCRIPTION

Referring to the drawings, wherein like reference numbers refer to likecomponents, FIG. 1 illustrates a hybrid powertrain 10 configured tolaunch and propel a vehicle, i.e., to operate the vehicle in all speedranges between low and high road speeds. The hybrid powertrain 10includes multiple power sources, which include an internal combustionengine 12, a first electric motor/generator 14, and a second electricmotor/generator 16, all connected to an electro-mechanical drive unitthat is depicted as an “electrically variable transmission” (EVT) 18.

The powertrain 10 additionally has an energy storage system thatincludes one or more batteries that are not specifically shown, butknown by those skilled in the art. The energy storage system isoperatively connected to the first and second motor/generators 14, 16such that the motor/generators may transfer torque to or receive torquefrom the engine 12. Although not shown, the powertrain 10 also includesa controller or an electronic control unit (ECU). The controller isoperatively connected to the power sources and to the energy storagesystem to control the distribution of torque from the power sources tothe EVT 18.

As is known by those skilled in the art, an “electrically variabletransmission” constitutes a transmission planetary gear trainoperatively connected to each of the engine 12, the firstmotor/generator 14, and the second motor/generator 16. Channelingrespective torques of the engine 12 and the two motor/generators 14 and16 to different members of the planetary gear train permits one of thepower sources to either assist or balance the operation of any of theother two. Thus, the combination of one engine 12 and twomotor/generators 14 and 16 operatively connected to the EVT 18 allowsspeeds and torques of the engine and motor/generators to be controlledand selected independently in order to power a subject vehicle moreefficiently.

Although the hybrid powertrain 10 as shown includes the engine 12, theEVT 18 may also be connectable solely to the first and second electricmotor/generators 14, 16. In such a case, the powertrain 10 would nolonger be a hybrid type, but would become purely electric, and the EVT18 may then be broadly described as an electro-mechanical drive unit.For simplicity and clarity, the remainder of the present descriptionwill refer to the electro-mechanical drive unit as EVT 18 beingconnected to the engine 12, as well as to the motor/generators 14, 16.Additionally, the connections of the hybrid powertrain 10, to bedescribed in greater detail below, may permit an overall decrease intorque requirement from the combination of the first and the secondmotor/generators 14 and 16 while affording acceptable vehicleperformance, as compared with other systems.

The EVT 18 includes two planetary gear sets represented in lever diagramform in FIG. 2. A lever diagram is a schematic representation of thecomponents of a mechanical device such as an automatic transmission.Each individual lever may represent an individual planetary gear set, acompound planetary gear arrangement having two or more interconnectedplanetary gear sets, or an external gear set. In the planetary gear setlever, the three basic mechanical components of the subject gear set,i.e., the sun gear, planet gear carrier, and ring gear members, are eachrepresented by a junction point on the particular lever. Therefore, atypical single planetary gear set lever contains three junction points:one for the sun gear member, one for the planet gear carrier member, andone for the ring gear member. The relative length between the junctionpoints of each planetary gear set lever can be used to represent thering-to-sun gear ratio of each respective gear set. These lever ratios,in turn, are used to vary the gear ratios of the transmission in orderto achieve appropriate ratios and ratio progression. Mechanicalcouplings or interconnections between the junction points of the variousplanetary gear sets are illustrated by thin, horizontal lines and torquetransmitting devices such as clutches and brakes are presented asinterleaved fingers. If the device is a brake, one set of the fingers isgrounded. Further explanation of the format, purpose and use of leverdiagrams can be found in SAE Paper 810102, authored by Benford, Howardand Leising, Maurice, “The Lever Analogy: A New Tool in TransmissionAnalysis” (1981), which is hereby fully incorporated by reference.

As may be seen in FIGS. 1 and 2, the EVT 18 includes a compound-splitplanetary gear arrangement 20. In general, as known by those skilled inthe art, a four-junction point lever, as shown in FIG. 2, is establishedby providing two separate fixed connections, i.e., pairings, between amember of one planetary gear set and a member of another planetary gearset. Such fixed connections may, for example, be provided between aplanet carrier of one gear set and a ring gear of another gear set, orbetween a planet carrier of one gear set and a sun gear of another. Whena single such fixed connection is employed, the subject connectionserves to reduce the maximum number of separately rotating inertias(about a common central axis) from six to four, and the total degrees offreedom from four to two. Thus constrained, the compound-split planetarygear arrangement 20 provides, in order of rotational speed, first,second, third, and fourth junction points. However, as understood bythose skilled in the art, various compound planetary gear arrangementsmay be constructed to provide a four-junction point lever that willaccomplish such a result, and place them within the scope of the leverdiagram of FIG. 2.

As shown in FIG. 1, the compound-split planetary gear arrangement 20includes a first planetary gear set 22 interconnected with a secondplanetary gear set 24 and includes two members of the first planetarygear set being operatively connected to two members of the secondplanetary gear set. As may be seen in FIG. 2, a lever 26 representingthe compound-split planetary gear arrangement 20 includes a first,second, third, and fourth junction points 26-1, 26-2, 26-3, and 26-4,respectively. The first junction point 26-1 represents or is defined bythe first member of the first planetary gear set 22, the second junctionpoint 26-2 is defined by the second member of the first planetary gearset interconnected with the first member of the second planetary gearset 24, the third junction point 26-3 is defined by the third member ofthe first planetary gear set interconnected with the second member ofthe second planetary gear set, and the fourth junction point 26-4 isdefined by the third member of the second planetary gear set.

As additionally shown in FIG. 1, the first gear set 22 includes a ringgear member 28, a carrier member 30, and a sun gear member 32.Furthermore, the second gear set 24 includes a ring gear member 34, acarrier member 36, and a sun gear member 38. As shown in FIG. 2, andconsistent with the above structure of the first and second gear sets22, 24, the first junction point 26-1 may represent the ring gear member28 of the first gear set 22. Additionally, the second junction point26-2 may represent the carrier member 30 of the first gear set 22interconnected with the ring gear member 34 of the second gear set 24.The third junction point 26-3 may represent the sun gear member 32 ofthe first gear set 22 interconnected with the carrier member 36 of thesecond gear set 24. Finally, the fourth junction point 26-4 mayrepresent the sun gear member 38 of the second gear set 24. Accordingly,the first planetary gear set 22 and the second planetary gear set 24 areconnected such that the resultant structure produces a four-junctionpoint lever that includes the junction points 26-1, 26-2, 26-3, and26-4, although the individual gear set members do not necessarily haveto be connected in the order presented above.

As shown in FIG. 3, the lever 26 may also be represented by twoindividual levers 39-1 and 40-1 that may correspond to the firstplanetary gear set 22 and the second planetary gear set 24,respectively. Accordingly, in FIG. 3 the junction points 26-2 and 26-3are represented by fixed interconnections, such that the resultantstructure effectively generates a four-junction point lever, similar tothat shown in FIG. 2. As such, the powertrain 10 shown in FIG. 1 is aspecific embodiment of a powertrain 10 represented by the lever diagramsshown in FIGS. 2 and 3. Accordingly, the EVT 18 as shown in FIG. 1 isrepresented by a schematic stick diagram and depicts a specificcompound-split planetary gear arrangement 20 that corresponds to and isreflected by the lever diagrams of FIGS. 2 and 3. Although a specificpowertrain 10 is represented in FIG. 1, it will be understood that theparticular embodiment is simply exemplary in nature, and otherpowertrain arrangements within the scope of the lever diagrams of FIGS.2 and 3 are also contemplated.

As may be seen in FIG. 1, the engine 12 and the first motor/generator 14are disposed on a common first rotating axis 41 and the secondmotor/generator is disposed on a second rotating axis 42, wherein thefirst axis is substantially parallel to the second axis. The EVT 18additionally includes a gear-train 44. The gear-train 44 is configuredto operatively connect the second motor/generator 16 to thecompound-split planetary gear arrangement 20 at the first junction point26-1. The gear-train 44 may be configured as either a single-stage or atwo-stage parallel shaft gear set.

With continued reference to FIG. 1, the engine 12, the firstmotor/generator 14, and the second motor/generator 16 are operativelyconnected to the EVT 18 via an input member arrangement, which transmitstorque from the power sources to the compound-split planetary geararrangement 20. The input member arrangement includes an output shaft ofthe engine 12, which serves as an input member 46; a rotor of the firstmotor/generator 14, which serves as an input member 48; and a rotor ofthe second motor/generator 16, which serves as an input member 50. Theinput member 46 is configured to provide engine torque to the EVT 18.The input member 48 and input member 50 are each configured to providetorque from the first motor/generator 14 and the second motor/generator16, respectively, to the EVT 18. As may be seen in FIGS. 2-3, the inputmember 46 is continuously connected to the third junction point 26-3,the input member 48 is continuously connected to the fourth junctionpoint 26-4, and the input member 50 is continuously connected to thejunction point 26-1. The EVT 18 also includes an output member 52. Theoutput member 52 is continuously connected to the second junction point26-2 and is configured to provide output torque from the compound-splitplanetary gear arrangement 20 for launching and propelling the vehicle.As shown in FIG. 1, the output member 52 may be configured as a chaindrive member that connects the carrier member 30 to a differential unit53. The output member 52 may also be configured as a gear drive.

As may be seen in FIGS. 1-3, the EVT 18 also includes a stationarymember such as a transmission case or housing 54. The third junctionpoint 26-3 is selectively connectable with the housing 54 via anengageable torque-transmitting device 56, to thereby ground the junctionpoint 26-3. The torque-transmitting device 56 may be selectively engagedand disengaged via an electrically actuated device, such as a solenoid.Additionally, the torque-transmitting device 56 may be configured eitheras a band, a roller-ramp one-way-clutching, a dog clutch, or a spragtype of a brake. Accordingly, the torque-transmitting device 56 may beused to brake the third junction point 26-3 relative to the housing 54.The electrically actuated torque-transmitting device 56 permits reducedefficiency losses in the hybrid powertrain 10, as well as in a purelyelectric powertrain application, i.e., sans the engine 12. Additionally,the electrically actuated torque-transmitting device 56 enablesincreased drive torque capability for the purely electric powertrainapplication.

A hybrid powertrain 110 is depicted in FIG. 4. The hybrid powertrain 110is similar to the hybrid powertrain 10 shown in FIG. 1 in that thehybrid powertrain 110 may also be represented by the lever 26 shown inFIG. 2, and is therefore another embodiment of the subject wide-nodeEVT. The hybrid powertrain 110 includes an EVT 118 with a compound-splitplanetary gear arrangement 120. As shown in FIG. 4, the compound-splitplanetary gear arrangement 120 includes a first planetary gear set 122interconnected with a second planetary gear set 124 and includes twomembers of the first planetary gear set being operatively connected totwo members of the second planetary gear set. As may be seen in FIG. 5,a lever 126 may also represent the compound-split planetary geararrangement 120. The lever 126 includes a first, second, third, andfourth junction points 126-1, 126-2, 126-3, and 126-4, respectively. Thefirst junction point 126-1 represents or is defined by the first memberof the first planetary gear set 122 interconnected with the first memberof the second planetary gear set 124, the second junction point 126-2 isdefined by the second member of the first planetary gear set, the thirdjunction point 126-3 is defined by the third member of the firstplanetary gear set interconnected with the second member of the secondplanetary gear set, and the fourth junction point 126-4 is defined bythe third member of the second planetary gear set.

As additionally shown in FIG. 4, the first gear set 122 includes a ringgear member 128, a carrier member 130, and a sun gear member 132.Furthermore, the second gear set 124 includes a ring gear member 134, acarrier member 136, and a sun gear member 138. As shown in FIG. 5, andconsistent with the above structure of the first and second gear sets122, 124, the first junction point 126-1 may represent the ring gearmember 128 of the first gear set 122 interconnected with the ring gearmember 134 of the second planetary gear set 124. Additionally, thesecond junction point 126-2 may represent the carrier member 130 of thefirst gear set 122. The third junction point 126-3 may represent the sungear member 132 of the first gear set 122 interconnected with thecarrier member 136 of the second gear set 124. Finally, the fourthjunction point 126-4 may represent the sun gear member 138 of the secondgear set 124. Accordingly, the first planetary gear set 122 and thesecond planetary gear set 124 are connected such that the resultantstructure produces a four-junction point lever that includes thejunction points 126-1, 126-2, 126-3, and 126-4, although the individualgear set members do not necessarily have to be connected in the orderpresented above. As shown in FIG. 5, the lever 126 may be represented bytwo individual levers 139-1 and 140-1 that may correspond to the firstplanetary gear set 122 and the second planetary gear set 124,respectively. Furthermore, the lever 126 may also be represented by thelever 26 depicted in FIG. 2.

A particular benefit of the described arrangement of the first, second,third, and fourth junction points 26-1, 26-2, 26-3, 26-4 of the EVT 18and the junction points 126-1, 126-2, 126-3, 126-4 of the EVT 118 isthat the subject EVTs are capable of providing a wide-node gear ratiospread, as shown by the graph shown in FIG. 6 and which will bedescribed in greater detail below. As employed herein, the concept of“node width” represents the distance traveled by the vehicle per eachrevolution of the engine 12, and the term “wide-node” is indicative ofthe distance traveled by a vehicle employing the EVT 18 or EVT 118 ascompared to a vehicle employing a typical single-mode EVT.

FIG. 6 shows a graph 64 of electrical power path magnitude as a fractionof engine torque used to drive the vehicle versus the vehicle distancetraveled per engine revolution in meters traced by a curve 70. Theelectrical power path magnitude is shown on the Y-axis of the graph 64and is represented by numeral 65, while the vehicle distance traveledper engine revolution is shown on the X-axis of the graph and isrepresented by numeral 67. Additionally, the graph 64 compares nodewidths of exemplary embodiments of the EVT 18 and EVT 118 which arerepresented by a distance 66 between mechanical points or nodesidentified by letters A and B and a distance 68 between pointsidentified by letters D and E plotted on the curve 70. In a specificexample, the distance 66 traveled by the vehicle per each revolution ofthe engine 12 with the EVT 18 and EVT 118, when electric power path(from the first and second motor/generators 14, 16) is zero, exceedsapproximately 0.8 meters. As shown, for the same configuration, thedistance 68 traveled by the vehicle per each revolution of the engine 12when electric power from the first and second motor/generators 14, 16 isapproximately equal to a fraction of engine power identified by letter Cand exceeds 1.2 meters. By comparison, in a typical single-modecompound-split EVT the distance 66 is generally around 0.5 meters, whilealso having the distance 68 of under of 1.2 meters. Accordingly, thegreater distance 66 for the EVT 18 and EVT 118 than for a typicalrepresentative single-mode compound-split EVT identifies the EVT 18 andEVT 118 as having a wider-node gear ratio spread.

As a result, the EVT 18 and EVT 118 are capable of providing at least a3 to 1 gear ratio spread between the torque-transmitting device 56(i.e., the input member 46) and the ring gear member 34 (i.e., theoutput member 52). Furthermore, the highest numerical gear ratio of theEVT 18 and EVT 118 having such an arrangement of the first, second,third, and fourth junction points 26-1, 26-2, 26-3, 26-4 may haveapproximately 4 to 1 as its highest numerical gear ratio andapproximately 0.7 to 1 as its lowest numerical gear ratio. As a result,the first motor/generator 14 may be sized differently, i.e., bephysically smaller, than the second motor/generator 16. Accordingly, thefirst motor/generator 14 may be configured to generate less torque thanthe second motor/generator 16. Additionally, each of the first andsecond motor/generators 14, 16 may be configured with solid cores andemploy non-rare earth magnets which are significantly more ubiquitousand less expensive than rare earth type.

As shown in FIGS. 1 and 4, each of the EVT 18 and EVT 118 also includesa first hydraulic pump 58 and a second hydraulic pump 60. The first andthe second hydraulic pumps 58, 60 are configured to supply pressurizedfluid to lubricate the compound-split planetary gear arrangement 20, aswell as the engine 12 and the first and second motor/generators 14, 16.As shown, the first pump 58 is operatively connected to the thirdjunction point 26-3 and the second pump 60 is operatively connected tothe output member 52, however, the positions of the two pumps may beinterchanged. Each of the EVT 18 and EVT 118 also includes a damper 62.The damper 62 is operatively connected to the engine 12 and isconfigured to absorb torsional vibrations generated by the engine beforesuch vibrations may be transmitted to the compound-split planetary geararrangement 20 via the input member 46.

The preceding configurations of the EVT 18 and EVT 118 are costeffective single-mode compound-split electro-mechanical drive units thatembody advantages of a two-mode system that provides a first mode forlaunching a vehicle from rest and a separate second mode for propellingthe subject vehicle at higher speeds, but eschews the two-mode system'smechanical and controls complexity. Accordingly, each of the EVT 18 andEVT 118 is a single-mode compound-split electro-mechanical drive unitthat enables sufficient torque to be generated and channeled forlaunching and propelling the vehicle, as well as supports an enginestop-start function. Additionally, the EVT 18 and EVT 118 are capable ofproviding reduced losses in operating efficiency of the powertrain 10during both drive and electric regeneration of the vehicle's energystorage system operating modes. Moreover, because the EVT 18 and EVT 118are each an off-axis layouts, i.e., has the engine 12 and themotor/generator 14 disposed on the first rotating axis 41 while themotor/generator 16 is disposed on the second rotating axis 42, the EVTs18 and 118 are particularly suitable to front-wheel-drive vehicleapplications, where the powertrain 10 is situated substantiallytransversely with respect to longitudinal axis of the subject vehicle.

The detailed description and the drawings or figures are supportive anddescriptive of the invention, but the scope of the invention is definedsolely by the claims. While some of the best modes and other embodimentsfor carrying out the claimed invention have been described in detail,various alternative designs and embodiments exist for practicing theinvention defined in the appended claims.

The invention claimed is:
 1. An electro-mechanical drive unitconnectable with multiple power sources for launching and propelling avehicle, comprising: an output member; a stationary member; agear-train; a torque-transmitting device; a compound planetary geararrangement having a first junction point, a second junction point, athird junction point, and a fourth junction point; the power sourcesincluding: a first motor/generator; and a second motor/generator;wherein: the second motor/generator is operatively connected to thecompound planetary gear arrangement at the first junction point via thegear-train; the output member is operatively connected with the compoundplanetary gear arrangement at the second junction point; the firstmotor/generator is operatively connected with the compound planetarygear arrangement at the fourth junction point; the torque-transmittingdevice is engageable to ground the third junction point to thestationary member; the compound planetary gear arrangement includes afirst planetary gear set interconnected with a second planetary gearset; the first and second planetary gear sets each include a respectivefirst, second, and third member; and two of the members of the firstplanetary gear set are interconnected with two of the members of thesecond planetary gear set.
 2. The electro-mechanical drive unitaccording to claim 1, wherein the first junction point is defined by thefirst member of the first planetary gear set, the second junction pointis defined by the second member of the first planetary gear setinterconnected with the first member of the second planetary gear set,the third junction point is defined by the third member of the firstplanetary gear set interconnected with the second member of the secondplanetary gear set, and the fourth junction point is defined by thethird member of the second planetary gear set.
 3. The electro-mechanicaldrive unit according to claim 1, wherein the first junction point isdefined by the first member of the first planetary gear setinterconnected with the first member of the second planetary gear set,the second junction point is defined by the second member of the firstplanetary gear set, the third junction point is defined by the thirdmember of the first planetary gear set interconnected with the secondmember of the second planetary gear set, and the fourth junction pointis defined by the third member of the second planetary gear set.
 4. Theelectro-mechanical drive unit according to claim 1, wherein the first,second, third, and fourth junction points provide at least a 3 to 1 gearratio spread between the torque-transmitting device and the output. 5.The electro-mechanical drive unit according to claim 1, wherein thefirst motor/generator is disposed on a first rotating axis and thesecond motor/generator is disposed on a second rotating axis, andwherein the first axis is substantially parallel to the second axis. 6.The electro-mechanical drive unit according to claim 5, wherein themultiple power sources additionally include an internal combustionengine disposed on the first rotating axis and operatively connectedwith the compound planetary gear arrangement at the third junctionpoint.
 7. The electro-mechanical drive unit according to claim 1,wherein the torque-transmitting device is selectively engaged anddisengaged via an electrically actuated device.
 8. Theelectro-mechanical drive unit according to claim 1, wherein thetorque-transmitting device is one of a band brake, a roller-ramp brake,a dog clutch, and a sprag brake.
 9. The electro-mechanical drive unitaccording to claim 1, wherein the second motor/generator is configuredto generate greater torque and is physically larger than the firstmotor/generator, and wherein each of the first and secondmotor/generators employ non-rare earth magnets.
 10. Theelectro-mechanical drive unit according to claim 1, further comprising afirst hydraulic pump and a second hydraulic pump, wherein the firsthydraulic pump is operatively connected to the third junction point andthe second hydraulic pump is operatively connected to the output member.11. A hybrid powertrain for launching and propelling a vehicle,comprising: an engine; a first motor/generator; a secondmotor/generator; and a single-mode wide-ratio gear ratio spreadelectrically-variable transmission having: an output member; astationary member; a gear-train; a torque-transmitting device; and acompound planetary gear arrangement having a first junction point, asecond junction point, a third junction point, and a fourth junctionpoint; wherein: the second motor/generator is operatively connected tothe compound planetary gear arrangement at the first junction point viathe gear-train; the output member is operatively connected to thecompound planetary gear arrangement at the second junction point; theengine is operatively connected to the compound planetary geararrangement at the third junction point; the first motor/generator isoperatively connected to the compound planetary gear arrangement at thefourth junction point; the torque-transmitting device is engageable toground the third junction point to the stationary member; the compoundplanetary gear arrangement includes a first planetary gear setinterconnected with a second planetary gear set; the first and secondplanetary gear sets each include a respective first, second, and thirdmember; and two of the members of the first planetary gear set areinterconnected with two of the members of the second planetary gear set.12. The hybrid powertrain according to claim 11, wherein the firstjunction point is defined by the first member of the first planetarygear set, the second junction point is defined by the second member ofthe first planetary gear set interconnected with the first member of thesecond planetary gear set, the third junction point is defined by thethird member of the first planetary gear set interconnected with thesecond member of the second planetary gear set, and the fourth junctionpoint is defined by the third member of the second planetary gear set.13. The hybrid powertrain according to claim 11, wherein the firstjunction point is defined by the first member of the first planetarygear set interconnected with the first member of the second planetarygear set, the second junction point is defined by the second member ofthe first planetary gear set, the third junction point is defined by thethird member of the first planetary gear set interconnected with thesecond member of the second planetary gear set, and the fourth junctionpoint is defined by the third member of the second planetary gear set.14. The hybrid powertrain according to claim 11, wherein the first,second, third, and fourth junction points provide at least a 3 to 1 gearratio spread between the torque-transmitting device and the outputmember.
 15. The hybrid powertrain according to claim 11, wherein thefirst motor/generator and the engine are disposed on a first rotatingaxis, the second motor/generator is disposed on a second rotating axis,and the first axis is substantially parallel to the second axis.
 16. Thehybrid powertrain according to claim 11, wherein the torque-transmittingdevice is selectively engaged and disengaged via an electricallyactuated device.
 17. The hybrid powertrain according to claim 11,wherein the torque-transmitting device is one of a band brake, aroller-ramp brake, a dog clutch, and a sprag brake.
 18. The hybridpowertrain according to claim 11, wherein the first motor/generator andthe second motor/generator employ non-rare earth magnets.
 19. The hybridpowertrain according to claim 11, wherein the second motor/generator isconfigured to generate greater torque and is physically larger than thefirst motor/generator.
 20. The hybrid powertrain according to claim 11,further comprising a first hydraulic pump and a second hydraulic pump,wherein the first hydraulic pump is operatively connected to the thirdjunction point and the second hydraulic pump is operatively connected tothe output member.